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The placebo effect

The placebo effect is the sensation of feeling better after taking a ‘dummy drug’, simply because you expected it to work. Gather your family for this activity but make sure it is only you that reads the instructions, otherwise the results will be given away!  

the placebo effect

What you'll need:

  • Lemonade
  • Red or pink food colouring 
  • Clear cups or glasses (2 per person taking part)
  • Spoon
The adult in charge is responsible for ensuring children don’t drink anything they are allergic to.
A child with two different types of lemonade, one clear and one pink. The child has given the pink lemonade a thumbs up and the clear lemonade a thumbs down.

the placebo effect

What you need to do:

  • Pour some lemonade into each cup. You’ll need two cups per person taking part.

  • Add a small amount of red food colouring to one cup per person and stir with a spoon. The lemonade in these cups should now appear pink.

  • Gather your family! Explain that there are two different types of lemonade to try, one clear and one pink. Do not reveal that the two lemonades are the same, with the only difference being the food colouring!

  • Explain that the challenge is to taste the two drinks and determine which one is sweeter. They could make a prediction first and then they can go ahead and taste each drink.

  • Ask each person which drink they thought was sweeter, the clear one or the pink one.

  • After everyone has given their answer, reveal that the drinks are actually the same! You simply added food colouring to some of the lemonade to make it pink. Did anyone guess this? Or perhaps most people thought the pink lemonade was sweeter?

  • the placebo effect


    The science:

    We often expect red or pink foods and drinks to taste sweeter than those of other colours. This expectation can be powerful enough that we can experience these foods and drinks as tasting sweeter, even when they are not. Our expectations can be a problem when testing new drugs. Let’s find out why…

    Imagine you have a cold and you’re taking part in a trial to test a new drug that aims to cure the cold. You're given the new drug by a scientist. What would you expect to happen next? You’d probably expect to get better! This expectation can be enough to make you feel better, so it would be difficult to tell whether the drug really worked or not. 

    In a drugs trial, this problem is overcome by giving half of the volunteers the real drug and the other half a placebo. Volunteers won’t know which one they have received. At the end of the trial, scientists compare the two groups. If the volunteers given the real drug show greater improvement than the volunteers given the placebo, this shows that the drug has been effective and that it’s not just due to the expectations of the volunteers.



    A dummy drug, also known as a placebo, is something that looks like a real drug but it does not have an effect on the body. For example, an injection containing a mixture of salt and water could act as a placebo for a vaccine.   

    If someone is given a placebo and believes it is a real drug, they can often feel better despite the placebo being inactive. This is known as the placebo effect.  

    the placebo effect

    real science

    Science at the Crick

    Tuberculosis (TB) is a bacterial infection that mainly affects the lungs. Despite being curable, it is one of the world’s deadliest diseases with around 1.7 million deaths every year. Some people can be infected by TB without developing the disease. However, the disease may be triggered later on making the person very unwell. 

    In 2016, scientists from the Crick and other organisations developed and trialed a vaccine to prevent infected people developing the disease in the future. Around 3500 people took part in the trail, with half being given the new vaccine and the other half receiving a placebo. After two years the trial showed promising results – volunteers given the vaccine were half as likely to go on to develop the TB disease compared to those given the placebo. 

    More recently, placebos have played an important role in determining the effectiveness of the new COVID-19 vaccines. 

    Centre of the Cell

    This activity has been adapted with permission from Centre of the Cell

    Centre of the Cell logo


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