What are the side effects of starting HRT?

Last reviewed July 6, 2026 by Dr. Sapna Jadhav, General Physician. Sources from ACOG, NHS, Mayo Clinic, CDC, NICE, NIH, Cochrane, and peer-reviewed journals.

Bottom lineStarting HRT commonly causes breast tenderness, nausea, headaches, bloating, and irregular spotting, and nearly all of it settles within 3 months; persistent side effects are fixed by adjusting the dose, hormone type, or delivery route, while clot signs, new migraine with aura, or heavy unexpected bleeding warrant prompt medical attention.

Mild side effects are common in the first weeks of HRT, and most settle within 3 months as your body adjusts.

Common early side effects

• Breast tenderness or swelling - the most frequent one; usually eases by 3 months.
• Nausea and mild headaches - more common with estrogen tablets; taking them with food or at bedtime helps, and switching to a patch or gel often resolves them.
• Bloating and fluid retention - typically temporary.
• Leg cramps - common and usually mild; regular stretching helps.
• Irregular bleeding or spotting - expected in the first 3-6 months, especially on continuous combined HRT or after a hormonal IUD is placed.
• PMS-like symptoms during the progesterone phase of sequential HRT - bloating, irritability, low mood. Switching the progesterone type or delivery method usually fixes this.

Side effects by hormone

Roughly speaking, estrogenic side effects are breast tenderness, nausea, and headaches, while progestogenic ones are mood changes, bloating, and acne - knowing which side is causing trouble tells your clinician which half of the prescription to adjust.

The 3-month rule

Most starting side effects fade as your body adapts, which is why clinicians ask you to persist (if symptoms are tolerable) until the 3-month review before changing anything. Side effects that persist beyond 3 months are a reason to adjust the dose, hormone type, or delivery route - not to abandon treatment.

When not to wait

Contact your clinician promptly for: signs of a blood clot (painful swollen calf, sudden breathlessness, chest pain), a first-ever migraine with aura, very heavy bleeding, or any bleeding that starts after months of none - and go straight to emergency care for chest pain or breathlessness.

This is general information, not medical advice. Read the full guide: starting HRT and what to expect.

Log your side effects: menopause symptom score