These drugs work together to cause an effect greater than the sum of its parts. They aren't likely to cause an adverse or undesirable reaction when used carefully.

Effects are additive. The combination is unlikely to cause any adverse or undesirable reaction beyond those that might ordinarily be expected from these drugs.

One substance may reduce or counteract some of the effects of the other.

These combinations are not usually physically harmful, but may produce undesirable effects. Use caution.

There is considerable risk of physical harm when combining these substances. Use extreme caution.

These combinations are considered dangerous and should be avoided.

The interactions between these substances are not well documented.