The 12-year-old Dunedin boy has autism and the thick, yeasty spread is the only way his family can disguise medication to control his violent impulses and severe anxiety.
When Sanitarium announced in March that production of the spread had been halted because of earthquake damage at its Christchurch factory, his mother, Sharon, joined countless others hunting for supplies.
"I thought when the announcement was made that they were having me on," the Autism New Zealand service support co-ordinator said.
However, publicity the next day prompted her to rush to the supermarket, where she found none.
A retailer who heard of her situation put two jars aside, Moyles Supermarket found one, and two half jars and some single serves were also sent to the family.
However, as Luke went through about a 500g jar every week, supply was running low and Mrs Bain was worried.
Marmite was the only thing she could find to disguise the taste of his medication, which she sprinkled on toast or bread, and which enabled him to "function in his daily life".
Without medication, Luke could not sleep at night, his anxiety levels went "through the roof" to the point a trip to a restaurant would make him vomit, and he lost impulse control which could result in his "smashing his head against anything".
Because of his autism, he was "very sensitive" to the types of food he ate and because Marmite worked, she was scared to try anything else in case he reacted negatively.
"It's a big vicious cycle."
Last month, Sanitarium said it was unlikely Marmite would be back on shelves before November, because of additional damage found at the factory.
Mrs Bain had a simple plea: "Hurry up, Sanitarium."
