Tylenol Cold is a mixture of the following:

Acetaminophen

Chlorpheniramine

Dextromethorphan

Pseudoephedrine

The Chlorpheniramine is an anahistamine and will have a calming effect for many people.

The Pseudoephedrine is a deconjestant and can cause the opposite effest, can keep a person awake and nerves on edge.

The Dextromethorphan is a cough med and can cause drowsiness.

The Chlorpheniramine and Dextromethorphan together may very well cause you to be in a drowsy state.