Validity of a fast

During a fast, the daily routines and behaviors are to be modified.
Muslims have to abstain from certain Halal (Lawful) things and activities during the hours of fasting:

1. Eating
2. Drinking
3. Smoking
4. Having sexual relations with spouse
5. Loose talks, Abusing, Hurting others etc.

Taking medications orally or by injection or doing any the above, knowingly, nullifies the fast.

Islam is very flexible and all its rituals are designed only for the convenience of Muslims, and not to penalize them.

Unintentional mistakes, like eating in forgetfulness, even to one’s fill, or married couples getting intimate to an extent, will be overlooked and forgiven by Allah (God). It also applies to accidentally swallowing a little water while brushing or taking a bath.

Kaffarah (Penalty-Penitence)

If an obligatory fast in the month of Ramadan is knowingly missed without genuine reason, or it is broken without some valid reason, there is a strict Kaffaarah i.e. penitence for the missed fast.

One is required to observe 60 fasts continuously in lieu of the missed one.

However women are exempted from this continuity during their monthly cycle. But once it is over, they should resume fasting immediately.

Fidyah (Compensation)

A person who has become very weak due to old age or sickness, he or she is allowed to give Fidyah instead of fasting. It consists of one full meal of an adult human to the poor and the needy for each missed fast. Equivalent amount of money can be given to the poor and the needy instead of a meal.