What birth control method is least likely to cause weight gain in a female patient of reproductive age?

Birth Control Least Likely to Cause Weight Gain

The copper IUD (Cu-IUD) is the contraceptive method least likely to cause weight gain, as it contains no hormones and has no association with weight gain beyond normal age-related changes. 1

Weight-Neutral Contraceptive Options (Ranked)

First Choice: Copper IUD

• The copper IUD is the most weight-neutral contraceptive available because it has zero hormonal exposure and no mechanism to influence weight gain. 1
• Studies demonstrate that copper IUD users experience only age-related weight gain (approximately 1.5 kg over 12-18 months), which is the baseline expected in reproductive-age women not using hormonal contraception. 2
• Over 7 years of follow-up, copper IUD users gained weight at rates consistent with normal aging patterns in the general population, independent of the contraceptive method itself. 3

Second Choice: Barrier Methods

• Condoms, diaphragms, and cervical caps have no hormonal effects on weight whatsoever. 1
• These methods provide complete freedom from any metabolic effects but have lower contraceptive efficacy (18-28% pregnancy rates per year with typical use). 4

Third Choice: Combined Oral Contraceptives (COCs)

• Combined estrogen-progestin pills show no clear evidence of weight change in most users, though individual responses vary. 1
• When weight gain does occur with COCs, it is typically minimal and comparable to copper IUD users. 1
• COCs containing ≤35 μg ethinyl estradiol are recommended if hormonal contraception is preferred by weight-conscious patients. 1

Methods to Avoid When Weight is a Concern

Depot Medroxyprogesterone Acetate (DMPA)

• DMPA is consistently associated with the greatest weight gain among all contraceptive methods and should be avoided when weight is a primary concern. 1
• Women using DMPA gained significantly more weight than copper IUD users: 8.2 kg versus 4.9 kg over 5 years in one study. 5
• In the large ECHO trial, DMPA users gained 3.5 kg compared to 1.5 kg in copper IUD users over 12-18 months (difference of 2.02 kg, p<0.001). 2

Levonorgestrel Implant

• The LNG implant causes intermediate weight gain—more than copper IUD but less than DMPA. 2
• Women using LNG implants gained 2.4 kg versus 1.5 kg in copper IUD users over 12-18 months (difference of 0.87 kg, p<0.001). 2
• Over 5 years, LNG-IUS users gained 3.1 kg compared to 4.9 kg in copper IUD users, showing minimal difference. 5

Clinical Counseling Approach

When a patient prioritizes avoiding weight gain:

1. Recommend the copper IUD as first-line unless contraindications exist (current pelvic infection, unexplained vaginal bleeding, or Wilson's disease). 1, 6

2. If copper IUD is declined or contraindicated, offer combined oral contraceptives with ≤35 μg ethinyl estradiol as the next best hormonal option. 1

3. Explicitly counsel against DMPA if weight gain is the patient's primary concern, as the evidence consistently shows it causes the most weight gain. 1, 2

4. Measure baseline weight and BMI at contraceptive initiation—not to determine medical eligibility (all methods can be used in obese women), but to facilitate future discussions about weight changes and whether they relate to the contraceptive method. 4

Important Caveats

• All women of reproductive age tend to gain weight over time due to normal aging, independent of contraceptive use. 3
• The copper IUD does not prevent this age-related weight gain; it simply doesn't add to it through hormonal mechanisms. 3
• Individual responses to hormonal contraceptives vary considerably—some women gain weight with COCs while others do not. 1
• The levonorgestrel IUD (LNG-IUD) causes weight gain intermediate between copper IUD and DMPA, though one study showed similar gains to copper IUD over 5 years. 2, 5