In all OECD countries, pharmaceuticals are financed by a mix of public and private spending. Tax-funded schemes or social health insurance cover a significant amount of prescribed pharmaceuticals in most countries, sometimes complemented by private health insurance. Patients typically have to cover some part of the cost of prescription drugs themselves, although exemptions often exist for vulnerable segments of the population such as children, the elderly and patients suffering from certain chronic illnesses. Over-the-counter (OTC) pharmaceuticals are normally financed entirely by private households.