From another vet site (I would watch out for the 'aggressive' bit):
"Cannibis is derived from the dried leaves and flowers of the plant Cannabis sativa or hemp. Toxicity in dogs is usually as a result of ingestion rather than passive inhalation of smoke.
Signs include weakness, ataxia (especially hind limbs), drowsiness, dilated pupils, sensitivity to light, urinary and fecal incontinence. Behavioural changes include aggression agitation and barking
Treatment consists of preventing further absorption of the drug by gastric emptying and the use of intestinal absorbents. Supportive treatment is then given. Fatal outcomes are rare."
As he has been sick and ate the stuff last night then obviously he has absorbed/got rid of everything in his stomach by now. It will probably work through his system so he may have the runs later on.