Detrol LA is a type of medicine called an anticholinergic (or antimuscarinic) muscle relaxant. It works by relaxing the involuntary muscle that is found in the wall of the bladder. The muscle in the wall of the bladder is called the detrusor muscle. It can sometimes contract in uncontrollable spasms, and this is often referred to as having an overactive bladder. The overactive detrusor muscle can increase in the number of times you need to pass urine, or cause uncontrollable urges to pass urine, or involuntary leakage of urine (urinary incontinence). Tolterodine works by relaxing the detrusor muscle in the wall of the bladder. It does this by blocking receptors called cholinergic (or muscarinic) receptors that are found on the surface of the muscle cells. This prevents a natural body chemical called acetylcholine from acting on these receptors