How can the authenticity of heat sensitive ink on prescriptions be verified?

Verifying the authenticity of heat-sensitive ink involves observing its unique property of changing color in response to heat. This characteristic is specifically designed to ensure that alterations to the prescription, such as changes to the medication or quantity prescribed, can be detected easily. When rubbing the ink, the heat from the friction causes a color change, providing a quick and effective way to assess whether the prescription is genuine or tampered with.

In contrast, exposing the prescription to sunlight does not reliably indicate the authenticity of heat-sensitive ink, as sunlight's effect is inconsistent and could damage the document. Examining the texture of the ink would not provide clear information about its authenticity; surface texture may not correlate with tampering. Finally, verifying the expiry date pertains to the validity of the prescription but does not confirm the authenticity of the ink itself. Therefore, the best method to ensure the ink's authenticity is through the color change observed during rubbing, making this the correct choice.