Consider the following statements: 1. Heroin and cocaine differ in their predominant effects: heroin is depressant whereas cocaine is stimulant. 2. Cannabinoids and opioids act through distinct receptor systems. 3. Nicotine can alter cardiovascular function indirectly through adrenal hormones. 4. All abused substances share one identical molecular target and produce indistinguishable effects. How many of the above statements are correct?