asagohan wo tabenaide kusuri wo nomu to, hakike ga surukoto ga arimasu.

A useful breakdown is:

• 朝ご飯を食べないで = without eating breakfast
• 薬を飲むと = if/when you take medicine
• 吐き気がすることがあります = nausea may happen / you may feel nauseous sometimes

So the overall structure is:

• [Condition] 朝ご飯を食べないで薬を飲むと
• [Result] 吐き気がすることがあります

A very natural English rendering is:

• If you take medicine without eating breakfast, you may feel nauseous.

Here, ないで means without doing something.

So:

• 食べる = to eat
• 食べない = do not eat
• 食べないで = without eating

In this sentence, 朝ご飯を食べないで means:

• without eating breakfast
• or not eating breakfast and then...

It connects to the next action, 薬を飲む.

This is a very common question.

Both can sometimes be translated similarly, but the nuance is different:

• ないで often means without doing X
• なくて often suggests because not doing X or simply links ideas in a different way

So:

• 朝ご飯を食べないで薬を飲む = take medicine without eating breakfast
• 朝ご飯を食べなくて薬を飲む would sound less natural here if your main point is the sequence skipping breakfast, then taking medicine

In this sentence, ないで is the better choice because it clearly expresses not doing one action before doing another.

Here, と is a conditional, meaning something like:

• if
• when

So:

• 薬を飲むと = if/when you take medicine

But this と often has a special feel: it is commonly used when the result is seen as a natural consequence, general result, or typical outcome.

That fits this sentence well:

• If you take medicine without eating breakfast, nausea may occur.

It sounds like a general warning or medical explanation.

Because with this kind of conditional と, Japanese normally uses the plain dictionary form before it:

• 飲むと = if/when someone takes it

You can compare:

• 飲むと = if/when you take it; general result
• 飲めば = if you take it; more straightforward conditional
• 飲んだら = if/when you take it; often more situational or conversational

In this sentence, 飲むと sounds especially appropriate because it gives a general rule or tendency, like something you might see in instructions or warnings.

Here, ことがあります means:

• there are times when...
• it sometimes happens that...
• may...
• can sometimes...

So:

• 吐き気がすることがあります = you may feel nauseous
• more literally: there are times when nausea occurs

This is different from the pattern Vたことがある, which means have experience of doing something.

Compare:

• 日本に行ったことがあります = I have been to Japan before
• 吐き気がすることがあります = there are times when nausea occurs

So this sentence is about occasional occurrence, not past experience.

They are doing two different jobs.

1. 吐き気がする

   • 吐き気 = nausea
   • がする = is felt / occurs / can be sensed

   So 吐き気がする is a set expression meaning:

   • to feel nauseous
   • to have nausea

2. 吐き気がすることがある

   • Here, the whole idea 吐き気がすること becomes the thing that exists/occurs sometimes
   • So the second が marks こと as the subject of あります

You can think of it like this:

• [吐き気がする] こと = the event of feeling nauseous
• [吐き気がすること] が あります = that event sometimes happens

Because 吐き気 is a noun meaning nausea, and Japanese often uses the pattern:

• [sensation / symptom] + がする

Examples:

• 吐き気がする = feel nauseous
• 頭痛がする = have a headache
• めまいがする = feel dizzy
• 咳がする = have a cough

So 吐き気がする is a very natural medical-style expression.

Because both are the direct objects of verbs:

• 朝ご飯を食べる = eat breakfast
• 薬を飲む = take medicine

So:

• 朝ご飯を goes with 食べないで
• 薬を goes with 飲む

A learner may wonder whether は could be used instead. It could, but it would change the nuance.

For example:

• 朝ご飯は食べないで... would add contrast, something like as for breakfast, don’t eat it / without eating breakfast specifically...

In the original sentence, を is the neutral, straightforward choice.

The subject is omitted, which is very normal in Japanese.

From context, it most likely means something like:

• you
• a person
• someone taking the medicine

In English, we often have to supply the subject:

• If you take medicine without eating breakfast, you may feel nauseous.

But Japanese does not need to say あなたは unless there is a special reason to emphasize it.

It is overall polite-neutral, and the mixture is completely normal.

Why it looks mixed:

• 食べないで
• 飲む
• 吐き気がする

These are plain forms, but they are inside a clause and before grammar patterns like と and こと. Japanese normally uses plain forms there.

The final main verb is:

• あります = polite form

That makes the whole sentence sound polite enough for explanations, warnings, or instructions.

So this is not strange mixing. It is standard Japanese grammar.

Yes. You could say:

• 朝ご飯を食べずに薬を飲むと、吐き気がすることがあります。

This also means:

• If you take medicine without eating breakfast, you may feel nauseous.

The nuance is very similar. In many cases, ないで and ずに are both possible for without doing.

Very roughly:

• ないで is often more common and conversational
• ずに can sound a bit more formal or written

So the original sentence with 食べないで is very natural and easy to understand.