Leg swelling that begins a few days after starting an antihypertensive and becomes worse by evening is often a medication side effect, especially with calcium-channel blockers such as amlodipine, nifedipine, or felodipine. This is usually ankle/foot swelling on both sides and is caused by fluid shifting into tissues, not necessarily by the body retaining excess fluid. Amlodipine-related ankle edema is a well-recognized adverse effect. NHS amlodipine guidance and Specialist Pharmacy Service review discuss this.

Seek urgent medical care now if you have any of these:

Edema can also result from heart, kidney, liver, vein, or clot-related problems, so it should not automatically be assumed to be from the medicine.

Please tell me the exact antihypertensive name and dose, when it was started or increased, and whether the swelling is in both legs or one leg.

Yes, this pattern is very likely amlodipine-related ankle/leg edema. It commonly affects both feet/ankles, may start within days of beginning or increasing the dose, and typically becomes more noticeable toward evening. It is more frequent with higher doses, especially 10 mg. Amlodipine information from NHS lists ankle, foot, and leg swelling as a common side effect.

Get urgent assessment if the swelling is mainly one-sided, painful/red/warm, or you have shortness of breath, chest pain, sudden weight gain, or reduced urine.