Polyoxyethylene (20) sorbitan monooleate (polysorbate 80, Tween 80), a surfactant, has been widely used as a solvent for pharmacological experiments. 

It produced mild to moderate depression of the central nervous system with a marked reduction in locomotor activity and rectal temperature, exhibited ataxia and paralytic activity and potentiated the pentobarbital sleeping time. 

The results of the present study indicate that polysorbate 80 can neither be used as a solvent for isolated tissue experiments nor when considered for intravenous administration. However, polysorbate 80 can be employed safely as a vehicle for neuropsychopharmacological experiments in doses not exceeding 1 ml/kg.

Polysorbate 80 also opens up the blood-brain barrier allowing toxins into the brain, which would otherwise not reach the brain. These studies show the use of Polysorbate 80 in drug development as a means to cross the blood-brain barrier, which is there to protect us from these toxins crossing the barrier.