What are the risks of taking progesterone only?

Risks of Taking Progesterone-Only Contraception

Progesterone-only contraceptives have significantly fewer risks compared to combined hormonal contraceptives, with no increased risk of venous thromboembolism being their primary safety advantage. 1

Cardiovascular Risks

Venous Thromboembolism (VTE)

• Progestin-only contraceptives do NOT increase the risk of venous thromboembolism, unlike combined estrogen-progestin contraceptives 1
• Studies show relative risks of 0.90 (95% CI 0.57–1.45) for progestin-only pills and 0.61 (95% CI 0.24–1.53) for progestin IUDs 1
• This makes progesterone-only methods the preferred option for women with risk factors for thrombosis

Other Cardiovascular Considerations

• Unlike combined hormonal contraceptives, progestin-only methods are acceptable for women with cardiovascular risk factors, including those who:
  • Are aged ≥35 years who smoke 2
  • Have hypertension
  • Have diabetes or dyslipidemia

Hepatic Risks

• Progestin-only contraceptives are considered safe in women with compensated cirrhosis 1
• They should be avoided in decompensated cirrhosis due to concerns about impaired hormone metabolism 1
• No evidence suggests progestin-only methods increase liver enzymes or fibrosis progression 1

Bone Health Concerns

• Depot medroxyprogesterone acetate (DMPA) injections carry a black box warning for decreased bone density 1
• Bone density typically normalizes after discontinuation of DMPA 1
• Other progestin-only methods (pills, implants, IUDs) have minimal to no effect on bone density 1

Side Effects and Tolerability Issues

Common Side Effects

• Irregular bleeding patterns (most common side effect)
• Headaches
• Mood changes
• Weight changes
• Breast tenderness

Specific Formulation Concerns

• Micronized natural progesterone may cause drowsiness and dizziness 3, 4
• Some users report fatigue with synthetic progestins 4
• Fluid retention may occur with some formulations 4

Efficacy Considerations (Affecting Risk of Unintended Pregnancy)

• Progestin-only pills have higher typical failure rates (approximately 9%) compared to other methods 1
• Require strict adherence to timing of daily dosing 1
• DMPA injections have a typical failure rate of approximately 6% 1
• Subdermal implants have the lowest failure rate (0.05%) 1

Special Populations

Women with Rheumatic Diseases

• Injectable DMPA may have a higher VTE risk (RR 2.67 [95% CI 1.29–5.53]) than other progestin-only methods 1
• Not recommended for women with positive antiphospholipid antibodies 1

Women with Hepatic Adenomas

• Limited data on hepatic adenoma growth with progestin-only contraceptives 1
• Theoretical concerns exist but are based on older, higher-dose formulations no longer in use 1

Women with Breast Cancer History

• Progesterone-only supplementation should be avoided in women with current or past ER+ breast cancer 5
• Women at high risk for developing breast cancer due to family history or genetic factors (BRCA1/2 mutations) should proceed with caution 5

Practical Considerations

• Progestin-only pills require stricter adherence to timing than combined pills
• DMPA injections delay return to fertility for up to 18 months after discontinuation 1
• Levonorgestrel IUDs often reduce or eliminate menstrual bleeding, while copper IUDs (non-hormonal) may increase bleeding 1

When considering progesterone-only contraception, the primary advantage is the avoidance of estrogen-related risks, particularly VTE. The choice between different progesterone-only methods should be based on efficacy requirements, side effect profile, and individual health considerations.