Contraception: Methods, Effectiveness, Mechanisms, and Side Effects

Introduction

Contraception encompasses methods and devices used to prevent pregnancy. The US Centers for Disease Control and Prevention publishes the US Medical Eligibility Criteria (US MEC) and Selected Practice Recommendations (US SPR) for contraceptive use. Patient preference, medical eligibility, and effectiveness should guide method selection.

Effectiveness Ratings

Typical Use vs Perfect Use

Method	Typical Use Failure Rate (First Year)	Perfect Use Failure Rate (First Year)	LARC or User-Dependent
No method	85%	85%	N/A
Implant	0.05%	0.05%	LARC
Copper IUD (Paragard)	0.8%	0.6%	LARC
Hormonal IUD (Mirena, Kyleena, Liletta, Skyla)	0.1-0.4%	0.1-0.4%	LARC
Female sterilization	0.5%	0.5%	Permanent
Vasectomy	0.15%	0.10%	Permanent
Injectable (DMPA, Depo-Provera)	4%	0.2%	User-dependent
Combined OCP/patch/ring	7-9%	0.3%	User-dependent
Progestin-only pill	4-13% (est. varies)	0.3%	User-dependent
Diaphragm with spermicide	17%	6%	User-dependent
Male condom	13%	2%	User-dependent
Female condom	21%	5%	User-dependent
Fertility awareness-based methods	13-23%	2% (varies)	User-dependent
Withdrawal (coitus interruptus)	20%	4%	User-dependent
Spermicide alone	21%	16%	User-dependent

Long-Acting Reversible Contraception (LARC)

Copper IUD (Paragard)

Aspect	Detail
Duration	Up to 10-12 years
Mechanism	Copper ions are toxic to sperm and interfere with implantation; local inflammatory response
Hormones	None (non-hormonal)
Efficacy	>99%
Timing of insertion	Any time pregnancy can be reasonably excluded
Return to fertility	Immediate upon removal
Side effects	Heavier/longer periods, increased cramping, intermenstrual spotting
Advantages	No hormones, long duration, emergency contraception
Disadvantages	Increased bleeding/pain, need for trained insertion

Hormonal IUDs

Device	Levonorgestrel Dose	Duration	Uterine Size Requirement	Hormonal Effects
Mirena	52 mg (20 mcg/day)	8 years (FDA-approved 8); ACOG says up to 8	>6 cm sound	Significant reduction in bleeding; may cause amenorrhea in 20-50%
Kyleena	19.5 mg (17.5 mcg/day)	5 years	>6 cm sound	Lower hormone dose; less amenorrhea; good bleeding profile
Liletta	52 mg (same as Mirena)	8 years	>6 cm sound	Similar to Mirena; more affordable
Skyla	13.5 mg (14 mcg/day)	3 years	>6 cm sound	Lower dose; best for nulliparous women; more spotting initially

Contraceptive Implant (Nexplanon)

Aspect	Detail
Duration	3 years (may be effective for 4-5 years)
Hormone	Etonogestrel 68 mg (progestin only)
Mechanism	Inhibits ovulation, thickens cervical mucus, alters endometrial lining
Efficacy	>99.9% (most effective reversible method)
Placement	Subdermal in inner upper arm (non-dominant), inserted by trained clinician
Removal	Simple incision, local anesthetic; removal failure possible if deeply placed
Side effects	Irregular bleeding (most common reason for discontinuation); 20% amenorrhea; mood changes; weight gain; headache

Hormonal Contraceptives

Combined Oral Contraceptives (COC or OCP)

Aspect	Detail
Hormones	Ethinyl estradiol (10-35 mcg) + progestin (various)
Mechanism	Suppresses ovulation (primary), thickens cervical mucus, alters endometrium
Dosing regimens	21/7 (21 active, 7 placebo), 24/4 (24 active, 4 placebo), extended (84/7), continuous (365 active)
Efficacy	91-99.7%
Advantages	Cycle control, lighter periods, reduced dysmenorrhea, acne improvement, reduced ovarian/endometrial cancer risk, reduced ectopic pregnancy risk
Disadvantages	Daily pill, prescription needed, contraindications, side effects

Progestin-Only Pill (POP or Minipill)

Aspect	Detail
Hormones	Norethindrone 0.35 mg or Drospirenone 4 mg
Mechanism	Primary: thickens cervical mucus, thins endometrium, disrupts ovulatory cycle (partial)
Timing	Strict: same time daily (+/- 3 hours for norethindrone; 12-hour window for drospirenone)
Efficacy	91-99.3% (depends on adherence)
Advantages	No estrogen (safer for those with contraindications), lactationally safe, may breastfeed immediately
Disadvantages	Strict timing, irregular bleeding (especially norethindrone), less cycle control

Contraceptive Patch (Xulane, Twirla)

Aspect	Detail
Hormones	Ethinyl estradiol + norelgestromin
Regimen	1 patch weekly for 3 weeks, 1 patch-free week
Placement	Abdomen, buttock, upper arm, back (not on breast)
Efficacy	91-99.7%
Notes	Same contraindications as COC; may be less effective if weight >90 kg (198 lbs); visible, may cause skin irritation

Contraceptive Ring (NuvaRing, Annovera)

Aspect	NuvaRing	Annovera
Hormones	Ethinyl estradiol + etonogestrel	Estradiol + segesterone acetate
Regimen	3 weeks in, 1 week out (each month)	3 weeks in, 1 week out (for 1 year; reusable)
Duration	1 month per ring	1 year (13 cycles)
Placement	Vaginal ring	Vaginal ring
Efficacy	91-99.7%	91-99.7%
Advantages	Monthly, less systemic absorption, comfortable	Year-long, reusable

Injectable Contraception (DMPA, Depo-Provera)

Aspect	Detail
Hormone	Medroxyprogesterone acetate 150 mg (progestin-only)
Dose	150 mg IM every 13 weeks (or 104 mg SQ)
Mechanism	Suppresses ovulation, thickens cervical mucus
Efficacy	96-99.8%
Advantages	Private, every 3 months, may reduce seizure frequency in epilepsy, reduces sickle cell crises
Disadvantages	Weight gain (significant in some), delayed return to fertility (average 9-10 months), bone mineral density loss (reversible), irregular bleeding then amenorrhea, injection visits

Barrier Methods

Male Condom

Aspect	Detail
Material	Latex (most common), polyurethane, polyisoprene, lambskin (does not protect against STIs)
Efficacy	87-98%
STI protection	Yes (latex, polyurethane, polyisoprene; NOT lambskin)
Advantages	No prescription, widely available, STI protection, no systemic side effects
Disadvantages	User-dependent, breakage/slippage, reduced sensation for some

Female Condom

Aspect	Detail
Material	Polyurethane or nitrile
Efficacy	79-95%
STI protection	Yes
Advantages	Female-controlled, no prescription, can be inserted up to 8 hours before sex
Disadvantages	Difficult insertion for some, visible outer ring

Diaphragm and Cervical Cap

Aspect	Diaphragm	Cervical Cap (FemCap)
Material	Silicone	Silicone
Use with spermicide	Required	Required
Efficacy (with spermicide)	83-94%	71-86%
Duration	Up to 2 years	Up to 2 years
Fitting	Requires fitting by clinician	Requires fitting
Insertion	Up to 6 hours before sex	Up to 6 hours before sex
Leave in after sex	6 hours minimum	6 hours minimum

Spermicide

Aspect	Detail
Active ingredient	Nonoxynol-9
Forms	Gel, foam, film, suppository
Efficacy alone	72-84%
STI protection	None (frequent use may increase HIV risk due to vaginal irritation)
Advantages	OTC, no prescription
Disadvantages	Low efficacy alone, vaginal irritation, messiness

Fertility Awareness-Based Methods (FABM)

Method	Tracking	Efficacy (Typical/Perfect)	Notes
Standard Days Method	Calendar: abstain on days 8-19	88-95%	For cycles 26-32 days
Two-Day Method	Cervical mucus daily	86-96%	Requires instruction
Ovulation (Billings) Method	Cervical mucus changes	77-98%	Well-established
Symptothermal Method	Temperature + mucus + cervical position	80-99.6%	Most effective FABM
Basal Body Temperature (BBT)	Temperature only	76-98%	Confirms ovulation but cannot predict
Lactational Amenorrhea Method (LAM)	Breastfeeding + amenorrhea + <6 months	99% with perfect use	Only for first 6 months postpartum

Emergency Contraception (EC)

Method	Timing	Efficacy	Mechanism	Availability
Copper IUD	Up to 5 days	>99%	Inhibits implantation, toxic to sperm	Prescription/insertion
Ulipristal acetate (Ella)	Up to 5 days	<3 days: 95%; Days 3-5: 85%	Inhibits/delays ovulation	Prescription
Levonorgestrel (Plan B One-Step, Take Action)	Up to 3 days (72 hours), some efficacy to 5 days	Days 1: 95%; Day 2: 85%; Day 3: 58%	Delays ovulation	OTC (all ages)
Combined OCP (Yuzpe method)	Up to 5 days	75-89%	Delays ovulation	Prescription

Sterilization

Female Sterilization (Tubal Ligation / Salpingectomy)

Aspect	Detail
Methods	Tubal ligation, salpingectomy (preferred), hysteroscopic sterilization
Timing	Postpartum, interval (anytime), or during cesarean section
Efficacy	>99.5%
Reversibility	Possible but expensive and not guaranteed
Side effects	Surgical risks (infection, bleeding, organ injury)
Advantages	Permanent, no ongoing work
Regret rates	Overall: 6-13%; higher if young (<30) or performed at time of cesarean

Vasectomy (Male Sterilization)

Aspect	Detail
Procedure	Scrotal incision or no-scalpel technique; vas deferens divided/occluded
Efficacy	>99.9%
Time to effectiveness	3 months or 20 ejaculations (semen analysis confirms azoospermia)
Reversibility	Vasovasostomy possible but variable success (30-90% patency)
Side effects	Hematoma, infection, chronic testicular pain (1-2%)
Advantages	Office procedure, local anesthesia, no hormonal effects, most effective

Contraceptive Selection Guides

US MEC Categories

Category	Definition
1	No restriction (method can be used)
2	Advantages generally outweigh theoretical/proven risks
3	Theoretical/proven risks usually outweigh advantages (use with caution)
4	Unacceptable health risk (method not to be used)

Medical Eligibility by Condition

Condition	Combined OCP	POP	DMPA	Implant	LNG-IUD	Cu-IUD
Hypertension (controlled)	3	2	2	2	2	1
Hypertension (>160/100)	4	2	2	2	2	1
Migraine without aura	2	1	1	1	1	1
Migraine with aura	4	1	1	1	1	1
DVT/PE (current)	4	2	2	2	2	1
DVT/PE (history)	3	2	2	2	2	1
Breast cancer (current)	4	4	4	4	4	1
Diabetes (no vascular disease)	2	2	2	2	2	1
Diabetes (with vascular disease)	3-4	2	3	2	2	1
Liver disease (severe)	4	3	3	3	3	1
Obesity (BMI >30)	2	1	2	1	1	1
Postpartum <21 days (non-breastfeeding)	4	2	2	2	2	1
Breastfeeding (<6 weeks)	4	2	3	2	2	1
Smoking, age >35	4	1	1	1	1	1

Counseling for Side Effects

Common COC Side Effects

Side Effect	Usual Onset	Management
Nausea	First 1-3 cycles	Take with food, at bedtime; switch to lower estrogen or progestin-only
Breakthrough bleeding	First 3-6 cycles	Reassure; if persistent, consider higher estrogen COC, different progestin, or change method
Breast tenderness	First cycles	Supportive bra; decrease estrogen dose
Weight gain	Variable	Not proven (estrogen causes fluid retention); counsel
Mood changes	Variable	Trial different progestin; consider non-hormonal method
Headache	Variable	If migraine with aura: discontinue; monitor pattern
Libido changes	Variable	Trial different progestin; consider non-hormonal method

Progestin-Only Side Effects

Side Effect	Management
Irregular bleeding	Counsel (common); NSAIDs, tricyclic COC temporarily (POP + COC for cycle control)
Acne	Switch to COC or different progestin
Mood changes	Trial different progestin or non-hormonal method
Breast tenderness	Supportive; resolves over time