Can Flowmax cause swelling of the lower legs and ankles?

What you are experiencing is not listed as possible side effects, bare in mind that not all possible side effects are listed.

I suggest you contact your doctor.

For future refernce:

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using tamsulosin and call your doctor at once if you have any of these serious side effects:

penis erection that is painful or lasts 4 hours or longer;
severe dizziness; or
fainting.

Less serious side effects may include:

mild dizziness or drowsiness;
sleep problems (insomnia);
abnormal ejaculation, decreased sex drive; or
runny or stuffy nose, sore throat.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. You may report side effects to FDA at 1-800-FDA-1088.

Take care.