IV cocaine is less effective than oral ingestion.
http://cat.inist.fr/?aModele=afficheN&cpsidt=1840992
http://emedicine.medscape.com/article/813959-overview
edit i have found contradicting sources though:
Approximately 80-90% of injected cocaine is rapidly metabolized. Decreased hepatic perfusion, secondary to conditions, such as hypotension or low-output congestive heart failure (CHF), results in elevation of cocaine levels. A similar result may be observed in pregnant women, fetuses, infants, patients with liver disease, and elderly men, because their plasma cholinesterase activity is decreased. In addition, some people have a genetic deficiency of plasma pseudocholinesterase or a nutritional predisposition to abnormally low pseudocholinesterase levels. Some have postulated that these patients may metabolize cocaine slowly and have increased sensitivity to small doses of cocaine, which places them at risk for increased toxicity and sudden death. Evidence supporting this postulate is scant.